i'm searching for an easy way to merge two PNG images with transparency overlapping.
The end result should look like this:

For the output image i need the size 500x750 as a png with transparency.
a.png should be resized to 60% of the output image (or a fixed size) and placed in the bottom left corner.
b.png should be resized to 60% of the output image (or a fixed size) and placed in the top right order (behind a.png)
Both images also have transparency.
Thanks
Dieter